1. Field of the Invention
The present invention relates to a DC/DC converter.
2. Description of the Related
There is a conventional DC/DC converter which includes a terminal group, a reactor, a switching element series circuit, a charge-discharge capacitor, and a smoothing capacitor, in a state where the terminal group includes a first terminal, a second terminal, a third terminal, and a fourth terminal, and the switching element series circuit includes a first switching element, a second switching element, a third switching element, and a fourth switching element, which are connected in series. A connection point of the second switching element and the third switching element is connected to the first terminal via the reactor, and an opposite side of a connection point of the first switching element and the second switching element is connected to the second terminal, and the charge-discharge capacitor is connected between the connection point of the first switching element and the second switching element and a connection point of the third switching element and the fourth switching element, and the smoothing capacitor is connected to the switching element series circuit in parallel, and the switching element series circuit is connected to the third terminal and the fourth terminal, and the first terminal and the second terminal are used as low-voltage-side terminals, and the third terminal and the fourth terminal are used as high-voltage-side terminals, and a DC voltage is converted between the low-voltage-side terminals and the high-voltage-side terminals. A control device includes a first calculation means, a second calculation means, and an open-close control means. The first calculation means calculates a first calculation value in accordance with a difference voltage between a high-voltage-side voltage instruction value, which is a voltage instruction value at a high-voltage side, and a high-voltage-side voltage detection value, which is a voltage detection value at a high-voltage side, or in accordance with a difference voltage between a low-voltage-side voltage instruction value, which is a voltage instruction value at a low-voltage side, and a low-voltage-side voltage detection value, which is a voltage detection value at a low-voltage side. The second calculation means calculates a second calculation value in accordance with a difference voltage between a voltage instruction value of the charge-discharge capacitor and a voltage detection value of the charge-discharge capacitor. The open-close control means calculates an energization ratio in accordance with the first calculation value and the second calculation value, and controls an open-close operation of the first switching element, the second switching element, the third switching element, and the fourth switching element in accordance with the energization ratio (for example, refer to Patent Document 1).
Moreover, there is a non-insulated type DC/DC converter, as a conventional DC/DC converter according to another example, which includes at least two switching elements connected to a coil, and performs a DC power conversion in such a way that the two switching elements are reversely operated each other by a control circuit, in which the control circuit performs soft start control, in which on-duty time of one switching element is gradually increased, when an operation is started, and the other switching element is turned off during the soft start control (for example, refer to Patent Document 2).
[Patent Document 1]
Japanese Patent Publication No. 5457559
[Patent Document 2]
Japanese Patent Publication No. 3501226
However, in a DC/DC converter which is described in Patent Document 1, a phase difference between a gate signal of a first switching element and a gate signal of a second switching element is controlled as 180°, and a gate signal of the first switching element and a gate signal of a fourth switching element are controlled as a complementary relation, and a gate signal of a second switching element and a gate signal of a third switching element are controlled as a complementary relation, so that a duty ratio of the first switching element and a duty ratio of the third switching element cannot be set as 1, and a both-end voltage of a low-voltage side capacitor and a both-end voltage of a charge-discharge capacitor cannot be uniformalized. Moreover, when a voltage is increased and a high-voltage side voltage instruction value is rapidly varied to a low value which is a low-voltage side voltage level, a duty ratio of the third switching element and a duty ratio of the fourth switching element are rapidly increased, so that an over current, which is corresponding to a difference between both-end voltages of a low-voltage side capacitor and a high-voltage side capacitor, is passed between the low-voltage side capacitor and the high-voltage side capacitor, and a low-voltage side voltage and a high-voltage side voltage are uniformalized. Therefore, in this case, there is a fear in which a switching element or a capacitor is destroyed by an over current, and a reactor is deteriorated. In other words, the both-end voltages of the low-voltage side capacitor and the high-voltage side capacitor cannot be safely uniformalized without passing an over current.
Moreover, in a DC/DC converter which is described in Patent Document 2, a switching element, which is connected to a coil, is softly started, so that when the soft start operation is applied to the DC/DC converter, which is described in Patent Document 2, a Ci voltage (VCi) and a Cf voltage (VCf) are not varied during a soft start term. After that, when an operation is shifted to a normal operation and a switching element S1 is turned on, an over current, which is corresponding to a difference between the VCi and the VCf, is passed through a passage of Ci→L→S3→Cf→S1, so that there is a fear in which a switching element or a capacitor is destroyed by an over current, and a reactor is deteriorated.